The invention relates to a method for fully eliminating lattice defects in N-conductive zones of a semiconductor device which are generated by ion implantation of phosphorus and to an associated semiconductor device.
It is known that the implantation of impurities in a silicon lattice causes dislocations. Owing to these dislocations, leakage currents in silicon semiconductor devices are increased considerably, particularly in integrated circuits consisting of this material. In the article "Strain Compensation in Silicon by Diffused Impurities" by T. H. Yeh et al., J. Electrochem. Soc.: Solid State Science, January 1969, pp. 73 the introduction of impurities in silicon by means of thermal diffusion is discussed. It is concluded that during the diffusion of boron or phosphorus, whose atomic radii substantially differ from those of silicon, strains are produced which cause dislocations. Yeh et al. arrived at the conclusion that tin or germanium atoms, whose atomic radii are greater than that of the silicon, can compensate for strains in the silicon which are caused by thermally diffused boron or phosphorus, whose atomic radii are much smaller than that of the silicon.
It is also known that after the introduction of conductivity-determining ions at a dose on the order of 10.sup.14 /cm.sup.2 in silicon by means of ion implantation and subsequent annealing, defects are formed in the crystal lattice. The density of these defects can be decreased by a double implantation and a subsequent thermal processing. An article by N. Yoshihiro et al., "High Dose Phosphorus-Germanium Double Implantation in Silicon", Proceedings of the 4th International Conference of Ion Implantation, 1975, pages 572-576 disclosed that the defect density can be reduced when phosphorus and germanium ions are implanted in the silicon in a double implantation. The best results were obtained using a first annealing step in wet oxygen at 800.degree. C., and then a second annealing step in nitrogen at 1100.degree. C. The article indicates that the germanium dose has to amount to at least 25% of the phosphorus dose.
A disadvantage of the above described method is that germanium is unfavorable for ion implantation because, due to low isotope abundance, low ion current densities are obtained. This effect is of particular importance when germanium is used at the above mentioned high dosage. Double annealing is a complicated process, and the oxidation taking place in the first step can affect other areas of the semiconductor component. The high temperature of 1100.degree. C. used in the second step is disadvantageous because of the simultaneous diffusion of the phosphorus. The control of the ion profile at such temperatures is no longer determined by ion implantation parameters but exclusively by diffusion processes.
It is also known, as shown in U.S. Pat. No. 4,111,719 to S. R. Mader et al. that in spite of the similar atomic radii of arsenic and silicon, dislocations are generated in the crystal lattice during the ion implantation of arsenic into silicon. These dislocations can be considerably reduced by implanting germanium into the arsenic-doped silicon.
It can be concluded that it is known that the density of the defects in arsenic or phosphorus-doped areas of silicon which are formed during the diffusion or implantation of conductivity-determining ions can be reduced by implanting non-conductivity-determining ions, e.g. tin or germanium, and by subsequent annealing. The nonconductivity-determining ions, however, have to be implanted in a relatively high concentration to ensure crystal lattice compensation and a reduction of the resulting lattice strains.
It is the object of the present invention to fully eliminate the lattice defects in phosphorus doped areas of silicon which lattice defects have a highly negative influence on the effect of integrated circuits.
Another object of the invention is to provide a method of the above specified type which is characterized in that conductivity-determining ions are implanted additionally into the phosphorus-doped zones.